Sliding vane pump

ABSTRACT

In a sliding vane pump comprising a rotor supported in a housing and having vanes supported radially movably in radially extending slots of the rotor so as to be in contact with the inner surface of a contour ring which is rotatably supported in the housing and forms with the vanes suction pumping and pressure chambers for pumping and pressurizing a fluid, a pressure control arrangement is provided for limiting the pressure in the pumping chamber to the pressure present in the pressure chamber thereby to prevent the generation of noise upon coupling of the pumping chamber with the pressure chamber.

BACKGROUND OF THE INVENTION

The invention relates to a sliding vane pump including a rotor withvanes disposed in a pump housing including suction, pumping and pressurechambers formed between the vanes and the housing.

DOS 198 29 726 A1 discloses a sliding vane pump wherein the noisegenerated as a result of pressure pulses is reduced. In order to providefor a smooth pressure increase between the suction side and pressureside of the pump, transmission passages in the form of chambers areprovided which permit a return flow of the hydraulic fluid from thepressure chamber to the pumping chamber. In this way, a pressure jumpbetween the pumping chamber and the pressure side is reduced whereby thepressure pulsations are reduced, particularly with a high air content inthe oil being pressurized.

The patent publication DE 196 26 211 C1 discloses a sliding vane pumpwith a contour ring formed in such a way that the hydraulic fluid can bepre-compressed as a result of a volume reduction of the pumping chamber.A pressure jump between the pumping chamber and the pressure side of thepump cannot be eliminated with such an arrangement, at least not for aparticular operating point.

It is the object of the present invention to provide a sliding vane pumpwith a pre-compression in the pumping chamber which improves the noisebehavior of the pump over a large operating range.

SUMMARY OF THE INVENTION

In a sliding vane pump comprising a rotor supported in a housing andhaving vanes supported radially movably in radially extending slots ofthe rotor so as to be in contact with the inner surface of a contourring which is rotatably supported in the housing and forms with thevanes suction pumping and pressure chambers for pumping and pressurizinga fluid, a pressure control arrangement is provided for limiting thepressure in the pumping chamber to the pressure present in the pressurechamber thereby to prevent the generation of noise upon coupling of thepumping chamber with the pressure chamber.

If, for example, the pressure is higher in the pumping orpre-compression chamber than in the pressure chamber the arrangementprovides for a pressure reduction in the pre-compression chamber to thepressure level in the pressure chamber. By the in-coupling of the volumeof the pumping chamber into the pressure chamber, there are no pressureoscillations whereby noise development is prevented. The arrangementavoids the development of noise in the pressure range in an advantageousmanner also with changing pressures which are determined by theoperating pressure of a system to which the fluid is supplied.

The pre-compression pressure which can be achieved corresponds to aminimum operating pressure of a system to which the pressurized fluid isto be supplied. If the pumping chamber is so designed that the pressureachievable by the pre-compression corresponds to the maximum operatingpressure of the system to which the fluid is supplied over the wholeoperating range of the system being supplied, there is the same pressurein the pumping chamber at the time when the pumping chamber is placedinto communication with the pressure chamber so that, at this point,little or no noise is generated.

In a particular embodiment of the invention, the arrangement includes avalve via which the pressure in the pumping chamber can be reduced byplacing it in communication with the suction area. If the pressure inthe pumping chamber is higher than the pressure in the pressure chamberhydraulic fluid is released, in a controlled manner, to the suctionchamber. The valve includes a slide member and a spring. The pressurelimiting valve must have high dynamics; therefore a slide member of thepressure limiting valve consist preferably of aluminum. Since the volumeflows through the valve are very small, the slide member should also beof a relatively small design.

In a further embodiment of the invention, the arrangement comprisesvanes which delimit the pumping chamber and which are subjected to a lowvane pressure. If the pre-compression pressure of the pumping chamber ishigher than the pressure in the pressure chamber, the hydraulic fluidflows through a gap between a contour ring and a vane from the pumpingchamber to the suction and/or pressure chamber. To this end, a vanevacuum which determines the force with which the vane is engaged withthe contour ring, is to be adjusted such that the pressure in thepumping chamber is lowered to the level of the pressure in the pressurechamber. As soon as the force resulting from the vane vacuum effectiveon the front side of the vane disposed between the pumping and thesuction chamber is smaller than the force resulting from the pressure inthe suction and pumping chamber on the opposite front side of the vane,the vane lifts off the contour ring and a reduction of the pumpingchamber pressure is facilitated by a release flow of the hydraulic fluidfrom the pumping chamber to the suction chamber. By the same principle,the pressure is released from the pumping chamber by a flow of thehydraulic fluid from the pumping chamber to the pressure chamber. Assoon as the force from below the vane on the front side of the vanedisposed between the pumping chamber and the pressure chamber is smallerthan the force resulting from the pressure in the pumping- and pressurechambers on the opposite front side of the vane, the vane lifts off thecontour ring and a pressure equalization between the two chamber isfacilitated. The arrangement according to the invention can therefore beprovided very cost-effectively.

In a further embodiment of the invention, the arrangement includes acontour ring which is rotatable relative to the suction and pressurechamber whereby the pressure in the pumping chamber can be adjusted tothe same pressure present in the pressure chamber. By rotating thecontour ring relative to the suction and pressure chambers, the level ofthe pre-compression of the hydraulic fluid in the pumping chamber can bedetermined. The vanes of the sliding vane pump slide along the radiallyinner surface of the contour ring. A pumping chamber transports thehydraulic fluid from the suction to the pressure areas, the pumpingchamber being separated from the suction chamber and the pressurechamber over an angular range predetermined by the design of the pump.If in the range determined by the angular range, the radius of thecontour ring becomes smaller, the hydraulic fluid is pre-compressed by avolume reduction of the pumping chamber; if the radius remains constantthe volume and the pressure level remain constant. In accordance withthe invention, the contour ring is rotated during operation of the pumpsuch that the same pressure level is established in the pumping chamberand in the pressure chamber. In this way, no pressure changes occur withthe in-coupling of the pumping chamber into the pressure chamber.

Preferably, the contour ring is rotatable by a cylinder piston unit. Thecylinder-piston unit rotates the contour ring with respect to thesuction and pressure chambers. The cylinder-piston unit is supported onthe pump housing and is connected to the contour ring. By applyingpressure to the cylinder-piston unit the contour ring can be rapidlyrotated.

In a further embodiment, the contour ring is rotated by the pressuredifference in the suction and pressure chambers. The contour ring isrotatably supported. In the suction and the pressure areas differentpressure levels are present. The pressures in the suction and pressureareas and the pressure in the pumping chamber are effective on thesurfaces of the contour ring which delimit these areas. If for example,the surface areas, on which the pressure is effective in thecircumferential direction, are equal and the pressure in the pressurechamber is noticeably higher than in the suction chamber, a force iseffective on the contour ring which can be used for rotating the contourring relative to the suction and pressure chambers. Since the surfaceareas of the pumping chamber on which the pressure is effective in thecircumferential direction is very small in comparison with the effectivesurface areas in the suction and the pressure area, this force componentcan be essentially neglected. With this arrangement, the contour ringcan be rotated in an advantageous manner without an additional operatingelement.

Preferably, the contour ring is held in a predetermined position by aspring, which may be a coil spring, a leaf spring, a plate spring or anair spring. The spring is disposed between the contour ring and thehousing of the suction and the pressure chamber. The spring force isdirected opposite to a force which rotates the contour ring, for examplea force of a cylinder piston unit. By way of the spring characteristicthe angle of rotation of the contour ring is controllable.

The cylinder piston unit however may also be provided with a controlunit. The control unit comprises a slide member disposed in a housingand a spring. The control unit controls the cylinder-piston unit in sucha way that the pressure level present in the pumping chamber is adjustedto the same pressure level as is present in the pressure chamber. Thecontrol unit derives from the pressure in the pressure chamber thepressure for the cylinder piston unit. The level of the pressure iscontrolled depending on the difference of the pressure in the pumpingand the pressure chambers. Under the control of the slide hydraulicfluid is supplied to the suction chamber for avoiding hydraulic fluidlosses and cavitations.

In a particular embodiment of the invention, the vane pump includes twosuction, two pumping and two pressure chambers. With the arrangement, acompact sliding vane pump with high pumping volume can be provided in anadvantageous manner.

Further features and feature combinations will become apparent for thefollowing description of the invention on the basis of the accompanyingdrawings. The drawings show the various embodiments in a simplifiedmanner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a sliding vane pump,

FIG. 2 shows a partial area of a development of the contour ring of thesliding vane pump of FIG. 1 in a first embodiment,

FIG. 3 shows a partial area of a development of the contour ring of thesliding vane pump of FIG. 1 in second embodiment of the invention,

FIG. 4 shows a partial area of development of the contour ring of thesliding vane pump of FIG. 1 in a third embodiment of the invention,

FIG. 5 shows a partial area of a development of the contour ring of thesliding vane pump of FIG. 1 in a fourth embodiment of the invention,

FIG. 6 shows a variation of the arrangement shown in FIG. 5,

FIG. 7 shows a variation of the arrangement shown in FIGS. 6, and

FIG. 8 shows an arrangement for the amplification of the vane engagementpressure.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Identical component of the FIGS. 1 to 8 are designated below by the samereference numerals.

Sliding vane pumps are used in connection with various systems such assteering systems, brake systems, active wheel suspension systems ortransmissions because they are compact and relatively inexperience. FIG.1 shows schematically a design of a double action sliding vane pump 1. Arotor 2 with radially movable vanes 3 is arranged within a contour ring4. The sliding vane pump 1 includes two suction areas 5 and two pressureareas 6, which comprise each suction and pressure passages which are notshown, suction and pressure areas 11, 12 and suction and pressurechambers 7, 8. Two side plates which are not shown delimit the chambers7, 8, 9 formed by the vanes 3 and the contour ring 4 in axial direction.Into these side plates, the suction pockets 11 and the pressure pockets12 are formed which are in communication with the fluid suction andpressure passages. A shaft rotates the rotor 2 with the vanes 3 in thedirection of rotation 10. The operation of the sliding vane pump 1 willbe described below for one of the double action sides.

As the volume of the suction chamber 7 increases with the rotation ofthe rotor in the direction of the arrow 10 hydraulic fluid is suckedinto the chamber 7. A pumping chamber 8 at the same time moves thepreviously sucked in hydraulic fluid to the pumping area 6 while thepumping chamber 8 is in communication with neither of the suction andthe pressure pockets 11, 12. As soon as the, in the direction ofrotation 10, rear edge 17 of the vane 3 of the pumping chamber 8 reachesthe pressure pocket 12, the hydraulic fluid volume is coupled into thepressure area 6. The volume of the pressure chamber 9 then becomessmaller whereby the hydraulic fluid is pumped by way of the pressurepockets 12 into a pressure channel.

If the pressure in the pressure area 6 is noticeably higher than in thepumping chamber 8, pressure oscillation occur in the in-coupling phasewhich results in an increased noise generation of the sliding vane pump1. Particularly if the pumping chamber 8 is not fully filled byhydraulic fluid but includes also air, a spontaneous compression of thepumping volume 8 occurs during in-coupling with a high pressuredifference between the pumping and the pressure chambers 8, 9. Thisresults in disturbing pumping pressure changes. Such a spontaneouscompression is avoided by ensuring that the pressures in the pressurearea 6 or, respectively, in the pressure chamber 9 and in the pumpingchamber 8 are essentially the same.

FIG. 2 shows schematically a sliding vane pump 1 in a first embodiment13. The circumference of the contour ring 4 the vanes 3 and the suctionand pressure pockets 11, 12 are shown in the diagram in a development sothat the volume of the chambers 7, 8, 9 is indicated over the angle orrotation p. The pockets 11, 12, which are arranged in the actual pumphousing in the side walls thereof are shown schematically in thefollowing figures adjacent the chambers 7, 8, 9. The radii changes ofthe contour ring 4 are exaggerated to show the clearly the volumechanges of the chambers. Analogous to FIG. 1, the volume of the chamber7 and of the chamber 7 a which is in the direction of rotation ahead ofthe chamber 7 increases whereby hydraulic fluid is sucked into thosechambers. The suction step is completed as soon as, with the continuedrotation of the rotor 2, the chamber 7 is no longer in communicationwith the suction pocket 11. In the pumping chamber 8, the hydraulicfluid is pre-pressurized. The pressure generated thereby is to beadjusted to the maximum operating pressure of the system to which thehydraulic fluid is to be supplied. The contour ring is therefore soshaped that the volume of the pumping chamber 8 is reduced upon rotationof the rotor. This arrangement makes it possible that, upon in-couplingof the pumping chamber 8 into the pressure area 6, no pressurepulsations occur. If the sliding vane pump 1 supplies a system with avariable operating pressure a device 13 lowers the pressure in thepumping chamber 8 to the level of that in the pressure chamber 9. Thearrangement 13 in the form of an over pressure valve comprises, disposedin a housing 16, a piston 14 and a spring 15. A first front end face 23of the piston 14 is subjected to the pressure of the pumping chamber 9and the force of the spring 15. As a result of the pressure in thepumping chamber 8, a first force component acts on the piston 14;because of the pressure in the pressure chamber 9 a second forcecomponent is provided. If the first force component is greater than thesecond force component and the spring force, then the piston 14 moves tothe right toward the spring 15. As a result, then the pumping chamber 8is placed into communication with the suction pocket 11, whereby thepressure in the pumping chamber is released until the second forcecomponent combined with the spring force is larger than the first forcecomponent and the piston 14 is again moved toward the left.

The spring 15 has the purpose of holding the piston in a definedposition. The spring force is very low so that the pressures in thechambers 8, 9 are controlled to be essentially the same. The apparatus13 reduces the pressure in the chamber 8 to the pressure level effectivein the chamber 9. Noises generated by pressure pulsation can beeffectively avoided even with changing pressures in the pressure pocket12 and, respectively, in the pressure channel 6.

In an embodiment which is simplified with regard to FIG. 2, but which isnot shown, the pressure pocket 12 is in communication with the pumpingchamber 8 only via a connecting line without the apparatus 13 disposedtherein. In this case also, the connection between the apparatus 13 andthe suction pocket 11 is omitted.

If for example the pressure in the pressure pocket 12 is higher than inthe pumping chamber 8, hydraulic fluid can flow from the pressure pocket12, via the connecting line, to the pumping chamber 8 and, as a result,reduce the pressure difference and the resulting oscillations. Thelength and the cross-section of the connecting line and the transferflow volume determined by the position of the control edges 18 should beoptimized for an efficient oscillation reduction.

FIG. 3 shows a second embodiment of an apparatus 13, which provides forequal pressures in the pumping or pre-compression chamber 8 and in thepressure chamber 9. The apparatus 13 comprises a cylinder-piston unit20, a spring 21, a control unit 22 and a rotatable contour ring 4. Thecylinder piston unit 20 is connected to the contour ring 4. By applyingpressure to the cylinder-piston unit 20, the contour ring 4 is rotatedrelative to the suction and pressure pockets 11, 12. By rotation of thecontour ring in the same or the opposite direction indicated by thearrow 27, the level of the pre-compression of the hydraulic fluid isadjustable. For example, the pre-compression is increased as the contourring 4 in FIG. 3 is rotated in a direction opposite to the arrow 27. Aspring 21 provides for a well-defined position setting of the contourring 4 and generates a return force. The spring 21 may be arrangedbetween the housing of the suction and the pressure pockets 11, 12 or,alternatively it may be arranged in the cylinder piston unit 20. Inorder to compensate for temperature changes, the spring 21 may also betemperature sensitive that is it may be a bi-metal spring or a memoryshape metal spring. Also, several springs may be provided in a parallelor in a serial arrangement. A control unit 22 determines the operatingpressure for the cylinder piston unit 20. The control unit 22 includes aslide valve 23 with a spring 24 which are arranged in a housing 25. Asmaster control pressure, the pressure of the pressure pocket 12 isapplied to the front surface 25 of the slide member, while the pressureof the pumping chamber 8 and the force of the spring 24 are applied tothe opposite front face 26.

Below, the operation of the apparatus 13 according to the invention isdescribed. If, for example, the operating pressure of the system to beoperated is low, no pre-compression should take place in the pumpingchamber 8. The spring 24 moves the slide member 23 into a position inwhich the line to the cylinder piston unit is connected to the suctionpocket 11 so that the spring 21 can rotate the contour ring 4 in thedirection of the arrow 27. The contour ring 4 is so designed that, inthis position, the volume of the pumping chamber 8 does not change. Assoon as, by an increase of the operating pressure, the force on thefirst front area 25 becomes larger than the spring force 20 and thepressure force on the second front face 26, the slide 23 moves andblocks the connection to the suction side.

At the same time, communication is established between the pressure inthe pressure pocket 12 and the cylinder-piston unit 20.

As a result of the pressure application to the cylinder piston unit 20,the contour ring 4 is rotated by an angle Δφ in a sense opposite to thedirection of the arrow 27 to the position 4′, so that pre-compression ofthe pumping volume is increased. The contour ring 4 is rotated, that isthe pressure in the pumping chamber is increased, until the pressure andspring force on the second front face 26 move the slide 23 back so thatthe communication with the cylinder piston unit 20 is again interrupted.The slide 23 maintains an equilibrium between the forces effective onthe first and the second front sides 25, 26, with a very small springforce is therefore approximately the same pressure provided at bothfront faces. As a result, also the same pressure is established in thepumping chamber 8 and the pressure chamber 9 whereby pressure pulses orpressure oscillation and the generation of noise associated therewith iseffectively avoided even with varying operating pressures.

FIG. 4 shows a third embodiment of an apparatus 13 according to theinvention. The apparatus 13 comprises a spring 21 and a contour-ring 4which is rotatable by an angle Δφ. The contour ring 4 is engaged by thespring 21, which is connected to the housing of the suction and pressurepockets 11, 12. The contour ring 4 is rotatably relative to the suctionand pressure pockets 11, 12 against the force of the spring 21. Contraryto the embodiment shown in FIG. 3, no cylinder piston unit is provided.The force for rotating the contour ring 4 is obtained directly from thepressures in the suction, the pumping and the pressure chambers 7, 8, 9.The force acting on the contour ring 4 can be determined by thefollowing equation:Fk=−A 7 ×p 7 +p 8 ×A 8 +p 9 ×A 9wherein:

-   -   p7 is the pressure in the suction chamber 7    -   A7 is the surface area of the contour ring 4 when exposed to the        suction pressure p7 in the circumferential direction,    -   p8 is the pressure in the pumping chamber 8,    -   A8 is surface area of the contour ring 4 on which the pumping        pressure is effective in the circumferential direction,    -   p9 is the pressure in the pressure chamber 9, and    -   A9 is the surface area of the contour ring 4 on which the        pressure in the chamber 9 is effective in the circumferential        direction.

The surface areas A7 and A9 can be calculated from the effective chamberheight multiplied by the chamber depth which is not shown in thedrawings. If the operating pressure of a system to be supplied withhydraulic fluid is small, the spring 21 moves the contour ring into aposition which does not provide for a pre-compression in the pumpingchamber 8. In this position, the area A8 has the value zero, and theareas A7 and A9 have the same size. The force Fk provided by thedifference of the pressures p7 and p9 is accommodated by the spring 21.

As the system operating pressure increases, also the force Fk becomeslarger as a result of the increasing pressure p9 and the contour ring 4rotates by an angle Δφ. In this position, the contour ring is designatedby the reference numeral 4′. As a result of the rotation, the pumpingchamber is increased by a volume 8′. In the pumping chamber 8, thehydraulic fluid is subjected to a pre-compression since the volume ofthe pumping chamber is decreased up to the coupling to the pressurepockets 12 by the volume 8′. Because of the small compressibility of thehydraulic fluid such as oil of 3×10⁻⁵/bar, the required compressionvolume 8′ is small. This is, with a loss-free calculation for a couplingpressure of 135 bar below 1% of the volume of the pumping chamber 8.With a rotation of the contour ring 4 by an angle Δφ therefore the areasA7 and A8 change only slightly so that this change is insignificant withrespect to the force Fk.

The system can be so adjusted that the pressure in the pumping chamber 8corresponds at the point of coupling exactly to the system operatingpressure and undesirable noises generated by pressure pulsations areavoided even if the system operating pressure changes, that is, if thepressures in the pressure area 6 change. The system is adjustedessentially by selecting the shape of the contour ring 4 and the spring21. For providing a suitable spring characteristic several springs maybe used in a parallel or in a serial arrangement.

In a modified embodiment which is not shown in the figures, for theadjustment of the pre-compression pressure in the pumping chamber 8, thesuction pocket and/or the pressure pocket 12 are rotatable relative tothe contour ring 4. For example, the side plates are rotatable by asuitable device in such a way that the same pressure level is obtainedin the pumping chamber and in the pressure chamber. Also a movableelement may be provided in the suction pocket 11 and/or the pressurepocket 12 by which the control edges 18 shown in FIGS. 1, 2 can bedisplaced. By an adjustment of the location of the control edges 18, thelevel of the pre-compression can be adjusted so that upon coupling ofthe pumping chamber 8 into the pressure chamber 9 no pressure pulsesoccur.

FIG. 5 shows a sliding vane pump with a vane 3 and a throttling devicefor controlling the pressure below the vane 3. A vane 3 is, in the shownposition, designated by the reference numeral 3′. The adjustment of thepressure in the pumping chamber 8 to the level of the pressure in thepressure chamber is obtained by a flow of the hydraulic fluid betweenthe vane 3′ and the contour ring 4. The vanes 3 are exposed to apressure below the vanes corresponding to the pressure in the pressurechamber 9. To this end a pressure pocket 12 disposed in a side plate isplaced into communication with the area 36 below the vane 3 by a passagewhich is not shown. The pressure is present between the rotating rotor 2and a stationary stator ring 33, which is connected to the side plate.The vane designated by the reference numeral 3′ separates the suctionchamber 7 from the pumping chamber 8. Because of the shape of the vanehalf of the face area in contact with the contour ring 4 is exposed tothe pressure in the suction chamber 7, while the other half is subjectedto the pressure in the pumping chamber 8. Since the suction pressure isrelatively small, the force component resulting therefrom is negligible.By a throttling device including throttles 28, 29, 30, the vane face atthe bottom of the vane 3′ is exposed to a pressure which is half thepressure in the pressure chamber 9. As a result, the vane 9′ is liftedoff the contour ring 4 when the pre-compression pressure in the pumpingchamber 8 exceeds the pressure in the pressure chamber 9. The hydraulicfluid flowing through the throttle 3 is returned to the suction pocket11 by way of a return line 31.

Hydraulic fluid flows from the pumping chamber 6 to the suction chamber7 until the pressure in the pumping chambers 8 equals that in thepressure chamber 9.

The throttling arrangement is such that from the area below the vane 3 ahydraulic volume flow is diverted and flows via the first and the secondthrottle 28, 29 to the area below the vane 3′. From this area, thehydraulic fluid volume flows via a third throttle 30 into a passage 31which extends to the suction pocket 11. If the flow resistance of thethrottles 28, 29 is twice that of the flow resistance of the throttle30, a pressure is established below the vane 3′ which is half as largeas the pressure in the pressure chamber 9.

By changing the flow resistances of the throttles 28, 29, 30 of coursealso the pressure below other vanes is adjustable. In this way, forexample, also the pre-compression pressure in the pumping chamber 8 isadjustable which is below or above the pressure level in the pressurechamber 9. Furthermore, also pressure losses which occur as a result ofleakages can be compensated for by changing the pressure below the vane3′.

FIG. 6 shows an arrangement wherein the throttling devices are omitted.The front surface of the vane 3′ for example which is in contact withthe contour ring 4 is so formed that the pressure of the pumping chamber8 is effective on the whole front surface. The whole area 36 below thevane is subjected to the pressure in the pressure chamber 9. As aresult, the vane 3′ is lifted off the contour ring 4 as soon as thepre-compression pressure in the pumping chamber 8 exceeds the pressurein the pressure chamber 9 whereby the pressure in the pumping chamber 8is adjusted to the level of the pressure in the pressure chamber 9.

The vane of the variant shown in FIG. 7 is so formed that the front sideof the vane 3″ which is in contact with the contour ring 4 is subjectedto a force resulting from the pressure in the pumping chamber 8. Thevane designated by the reference numeral 3″ separates the pumping andthe pressure chambers 8, 9. The area 36 below the vane is exposed to thepressure of the pressure chamber 9. If the pressure in the pumpingchamber 8 exceeds the pressure in the pressure chamber 9, the vane 9″ islifted off the contour ring 4 so that the pressures in the pumping andpressure chambers are equalized.

FIG. 8 shows an arrangement for amplifying the vane engagement pressure.The area 35, which is subjected to the pressure in the pressure chamber9, is increased by the provision of an amplifier piston 34. As a result,the force by which the vane 3 is biased toward the contour ring 4 isincreased. The space at the opposite side of the piston is incommunication with the suction pocket 11 so that no counter pressure canbuild up.

The arrangement may be used for example if only an insufficient contactpressure can be achieved because of leakages in the pumping chamber 8and/or the pressure chamber 9.

The various arrangements 13 described above for the adjustment of apressure of the same level in the pumping and in the pressure chamber 8,9 can of course be combined. All arrangements can be used in connectionwith single stroke and/or controlled sliding vane pumps.

1. A sliding vane pump, comprising a rotor (2) with vanes (3) radiallymovably supported on the rotor (2) in circumferentially spacedrelationship, a contour ring (4) extending around the rotor (2), thevanes being in contact with the contour ring (4) so as to form betweenthe rotor, the contour ring (4) and the vanes (3) suction chambers (7),pumping chambers (8) and pressure chambers (9) for pumping andpressurizing a fluid, the fluid being pre-compressed in the pumpingchamber (8), and an arrangement for providing in the pumping chamber (8)and in the pressure chamber (9) essentially the same maximum pumppressure level.
 2. A sliding vane pump according to claim 1, wherein themaximum pressure level corresponds to the maximum operating pressure ofa system to which the pressurized fluid is to be supplied.
 3. A slidingvane pump according to claim 1, wherein the pump includes a fluidsuction pocket (11) and a pressure pocket (12) and an arrangement (13)is provided including a valve disposed in a communication path betweenthe fluid pressure chamber (8) and the fluid suction pocket (11) fordischarging pressurized fluid from the fluid pumping chamber (8) whenthe fluid pressure in the fluid pumping chamber (8) exceeds the pressureof the fluid in the fluid pressure chamber (9).
 4. A sliding vane pumpaccording to claim 1, wherein means are provided for supplying fluidunder pressure to an area in the rotor below the vanes for biasing thevanes outwardly into contact with the contour ring (4).
 5. A slidingvane pump according to claim 3, wherein the contour ring (4) isrotatably supported for changing the angular position thereof relativeto the fluid suction, pumping and pressure chambers (7, 8, 9) forcontrolling the pressure in the pumping chamber (8) relative to thepressure in the pressure chamber (9).
 6. A sliding vane pump accordingto claim 5, wherein means are provided for rotating the contour ring (4)based on pressure differences in the suction, pumping and pressurechambers (7, 8, 9).
 7. A sliding vane pump according to claim 6, whereina cylinder piston unit (20) is connected to the contour ring (4) forrotating the contour ring (4).
 8. A sliding vane pump according to claim5, wherein a spring is connected to the contour ring (4) for biasing thecontour ring (4) into a predetermined angular position.
 9. A slidingvane pump according to claim 7, wherein the cylinder piston unit (20) isconnected to a control unit (22) for controlling the angular position ofthe contour ring (4).
 10. A sliding vane pump according to claim 1,wherein the sliding vane pump includes two suction, two pumping, and twopressure chambers (7, 8, 9).